Production of powdery maltose

ABSTRACT

Powdery crystalline maltose characterized by a high concentration of the beta-anomer of maltose monohydrate is produced by: 
     (1) obtaining a high purity maltose solution containing not less than 90% maltose and not more than 2.5% maltotriose by enzymatic saccharification of a liquefied starch solution having a low degree of hydrolysis; 
     (2) concentrating the high purity maltose solution to a solid content of 65 to 80%; 
     (3) adding seed crystals of beta-maltose monohydrate; 
     (4) precipitating maltose monohydrate crystals in a primary crystallization stage; 
     (5) spray drying the resulting massecuite to obtain a powdery product with a water content of 5.5-7.5%; and 
     (6) aging the powdery product at a temperature of 50°-75° C., relative humidity of 50-70% and absolute humidity of 45-185 g water/Kg dry air. 
     A product having low hygroscopicity is produced by this method.

The present invention relates to a method for producing powdery maltosewhich is of low hygroscopicity and readily soluble in water.

A known technique for producing powdery maltose generally comprises twosteps, i.e.

(1) saccharification of starch to obtain a saccharified solution and

(2) powderization of the saccharified solution,

and these steps are correlated with each other.

The generally well-known method to obtain a saccharified solution havingas high a maltose content as possible is one in which starch isliquefied by means of α-amylase (EC No. 3.2.1.1.), acid or mechanicaltreatment while controlling the hydrolysis to a minimized degree, andthen both β-amylase (EC No. 3.2.1.2.) and a debranching enzyme(pullulanase EC No. 3.2.1.41., isoamylase EC No. 3.2.1.68) are caused toact on the liquefied starch solution at the same time to obtain asaccharified solution. When this method is employed, the sugarcomposition of the resulting saccharified solution will be 85 to 92% ofmaltose, a small amount of glucose and more than several percents ofmaltotriose and oligosaccharides of several polymerization degrees. Withthe progress of hydrolysis in the liquefaction, there increases a chancein which chain molecules of an odd number of glucose units are formed,this being a reason for the formation of maltotriose (Japanese PatentPublication Nos. 37849/1971, 24060/1971, 13089/1972, 3937/1979,3938/1979, 9739/1977, etc.). In the above method, a liquefied starchsolution with an extremely low degree of hydrolysis and low viscosity isobtained by liquefying a starch solution having a starch concentrationof 20% or less by the mechanical liquefaction method, and therefore, ahigh-purity maltose solution of a low maltotriose content can beobtained by saccharifying said solution with β-amylase (e.g. of soybeanorigin) exhibiting a saccharification activity in the vicinity of 60° C.and a debranching enzyme of microbial origin. In this case,retrogradation of starch molecules can be prevented by adding a properamount of α-amylase at a proper time in the saccharification stage.Also, among microorganisms are those such as Streptomyces hygroscopicus,etc. which can produce enzymes which are α-amylase but are also capableof producing not less than 75% of maltose by the hydrolysis of starch.This enzyme not only produces maltose and maltotriose by the hydrolysisof starch, but also acts on the maltotriose to cut it into maltose andglucose, then produces maltotetraose from the resulting glucose and themaltotriose by transglucosidation and then cuts the maltotetraose intotwo molecules of maltose. It is also known that glucoamylase has ahigher affinity to high molecular substrates with a large reaction rate.By the utilization of a proper combination of the substratespecificities of these enzymes, a high-purity maltose-containingsaccharified solution of a low maltotriose content can be prepared. Asother methods, there may be mentioned those in which only β-amylase iscaused to act on a liquefied starch solution of the same low degree ofhydrolysis as above, or a proper amount of α-amylase is added in thecourse of the reaction, thereby producing a saccharified solutioncontaining 60 to 70% of maltose (based on the total sugar) and β-limitdextrin (molecule having a branch bond) as the rest. Removal of thisβ-limit dextrin therefrom will result in a high-purity maltose solution.However, also in this case, the amount of maltotriose increases with theprogress of hydrolysis on liquefaction, and in practice, severalpercents or more of maltotriose are produced as by-product.

Known methods for powderizing the above produced maltose-containingsaccharified solution include the so-called total sugar method,spray-drying method (Japanese Patent Publication Nos. 3937/1979 and23325/1979), crystal separation method and the like. The total sugarmethod is a method in which a saccharified solution having a maltoseconcentration of not less than 80% (based on the total sugar) isconcentrated to form β-maltose monohydrate crystals, thereby solidifyingthe whole system as a solid mass. This solidified product, after beingaged for a proper period of time, is chipped and sieved into a powder.The commercial products produced by this method contain 85% of maltose,about 5% each of maltotriose, glucose and dextrin and about 6% of water.It is however well known that, when said products are allowed to standin an atmosphere in which the temperature is 30° C. and the relativehumidity (hereinafter referred to as RH) is 80%, they take up about 3%water only after one day, reaching a water content of about 9 to 9.3%,and that they take up water to about 9% also when the temperature is 25°C. and the relative humidity is 80% [refer to Starch Science Handbook,p. 457 (1977), Asakura Shoten, Tokyo, Japan]. Further, such commercialproducts contain fine particles which, although sieved, take some timeto dissolve in water. For this reason, the sparingly soluble particleseven in a small amount cause a fatal defect in uses in which the powderis directly added without being dissolved in water and kneaded as inminced fish meat, chocolate, etc.

The spray-drying method can provide products superior in solubility, butthe amorphous or non-crystalline powder, because of its extremely highhygroscopicity, becomes a problem as a commercial product (StarchScience Handbook, p. 457, 1977, published by Asakura Shoten). For thisreason, a method has been proposed in which, after concentrating themaltose solution, the resulting massecuite containing partly depositedcrystals is spray-dried (Japanese Patent Publication No. 3937/1979). Theterm "Massceuite" as used here means a maltose syrup containingmicrocrystals of maltose. In this method, the saccharified solution isconcentrated to 70 to 80%, seed crystals are added at about 35° C. toform crystals over 1 to 3 days until the rate of crystallization reachesnot less than 35%. The resulting massecuite is sprayed into a dryingcolumn while feeding a hot dry air of 80° C. to 90° C. into the column,and the powdery product is slowly withdrawn on a conveying belt from thebottom of the column while blowing 40° C. warm air up from below thebelt. The dry powder thus obtained is filled in an ageing column, andits crystallization and drying are finished by passing warm air throughthe column for about 10 hours to obtain a powder having a water contentof 6%. This method, on considering its process, is a combination ofprimary crystallization, spray-drying and ageing intended to maintain acomplete crystal form. The present inventors also studied this method,and as a result thereof, found that, because it takes a long time forthe primary crystallization and ageing, design of continuous process isalmost impossible and also impractical in terms of cost. Further, theproduct is still high in hygroscopicity and therefore not practicallyuseful.

In view of the facts described above, the present inventors made anextensive study while referring to the already known methods with theobject of providing a continuous process for producing maltosecrystalline powders which have a low hygroscopicity, no adhesiveness,free-flowing good flowability and easy solubility and which can bekneaded, in its powdery form, into minced fish meat, chocolate, etc.,and as a result, have found that the desired objects can be attained bya combination of some particular conditions. The present inventors thusarrived at the present invention.

According to the present invention, there is provided a method forproducing powdery maltose characterized in that a high-purity maltosesolution, the sugar composition being not less than 90% of maltose andnot more than 2.5% of maltotriose, obtained by the enzymatic hydrolysisof a liquefied starch solution of a low degree of hydrolysis isconcentrated to a solid content of 65 to 80%, seed crystals are addedthereto and primary crystals are precipitated at a crystallizationtemperature of 25±5° C. until the degree of crystallization (i.e. as drymaltose based on the solid content in the massecuite) reaches 50±5%, theresulting massecuite is spray-dried to form maltose powder, which isthen aged under high temperature and high humidity conditions tocomplete the β-anomerization and crystallization of maltose monohydrate.

In a preferred embodiment of the above process, the spray-dryed product,immediately after the spray-drying, is subjected to ageing by exposingthe same to a high temperature high humidity atmosphere satisfying theconditions that the temperature is 50°-75° C., the relative humidity is50-70% and absolute humidity is 45-185 g. water/kg. dry air, to completethe β-anomerization and crystallization.

In any case it is preferable that the spray-drying is so conducted thatthe water content of the powder right after the spray-drying is5.5-7.5%.

When the viscosity of the massecuite after the primary crystallizationis too high it is preferable to add a proper amount of the same maltosesolution as mentioned above thereto to lower the viscosity at thecrystallization temperature to be not higher than 70,000 centipoises,before subjecting the same to the spray-drying.

The powderization according to the present invention may be said to bethe same as the known methods explained hereinbefore in that itcomprises the crystallization of primary crystals, spray-drying andageing. However the process of the present invention is novel anddistinctive in the selection and combination of the above mentionedparticular conditions.

The present invention will be explained in more detail as follows byreferring partly to the accompanying drawings wherein

FIG. 1 is a graph illustrating the relationship between thetemperature/humidity condition at ageing step and the specific rotationof the product, and

FIG. 2 is a graph illustrating the relationship between thetemperature/humidity condition at ageing step and water content of theproduct.

The present inventors have found some novel facts in the course ofcomparison and investigation of relationships between, on the one hand,the sugar composition of maltose solutions and, on the other hand, theprimary crystallizability, spray-dryability and ageability thereof andthe hygroscopicity and equilibrium water content of the product.

First, the present inventors have found that the maltotriose content ofa maltose solution exerts a considerable effect on the crystallizabilityof primary crystals, viscosity of the massecuite and hygroscopicity(equilibrium water content) of the product. Thus, it has been found thatthe effect of content of glucose, maltotetrarose and maltopentaose issmall as compared with that of the maltotriose content, but that, byreducing the maltotriose content in the maltose solution to not morethan 2.5% (based on the total sugar in the solution), the formation ofprimary crystals of maltose becomes very easy, and that the viscosity ofthe massecuite, at crystallization degree of 50±5% and Brix degree(hereinafter referred to as Bx) of 68 to 72 becomes not more than 40,000cp, whereby spray-drying of the massecuite becomes very easy.

Further, it has been found to be preferable that the spray-dryingcondition be regulated so that the water content of the spray-driedproduct is 5.5 to 7.5%, and that said product be aged in a hightemperature and high humidity atmosphere wherein, preferably, thetemperature is 50° to 75° C. the relative humidity is 50 to 70% and theabsolute humidity is 45 to 185 g water/kg dry air.

In order to obtain a solution of both low maltotriose content and highmaltose content, it is known that the starch concentration in thestarting material should be lowered and the enzyme should be used inwell selected conditions. However, practically, it is very difficult toobtain the desired object directly. Therefore, when control of themaltotriose content to not more than 2.5% is attempted as in the presentinvention, it is practical to subject the saccharified solution to achromatographic separation technique using adsorbents. Moreparticularly, there may be used the selective adsorption/elution methodwith anion-exchange resins (Japanese Patent Publication Nos. 4239/1981and 46290/1977) which is known per se. According to this method, anaqueous solution with an extremely high maltose purity (89 to 98% basedon the total sugar) can be obtained. However it is preferable to utilizea simulated moving bed system with porous Na-type cation-exchangeresins. A saccharified solution can be fractionated into maltose andhigher-order polymeric oligosaccharides than maltotriose by thesimulated moving bed method. For example, when a saccharified solutionwith a sugar composition of 60 to 70% of maltose the remaining componentbeing β-limit dextrin, as obtained by saccharifying the before mentionedliquefied starch solution of a low degree of hydrolysis with β-amylaseonly, is subjected to the separation procedure described above, it isdivided into two fractions under normal conditions, i.e. a maltosefraction of about 55 to 65% based on the total sugar and anoligosaccharide fraction of about 35 to 45% based thereon. And, the rateof fractionation to the maltose fraction of various saccharides is 70 to80% for maltose and 55 to 65% for glucose, while that of maltotriose andother oligosaccharides is only 8 to 15%, most of them moving to theoligosaccharide fraction. Consequently, this means that the maltosefraction not containing more than 2.5% of maltotriose is obtained by oneseparation operation in an amount of about 55 to about 65% based on thetotal sugar weight in the starting solution. The oligosaccharidefraction may be saccharified into glucose by the action of glucoamylasewhen it is added to a saccharification vessel for producing glucose, sothat it can be utilized without a loss.

Thus, by properly utilizing the above mentioned methods, there may beobtained a saccharified aqueous solution with a sugar composition of notless than 90% of maltose and not more than 2.5% of maltotriose by theenzymatic hydrolysis of a liquefied starch solution of a low degree ofhydrolysis (e.g. dextrose equivalent or DE value of less than 10,preferably 3-7) and subsequent separation of high molecularoligosaccharides. The high purity maltose solution is then subjected tothe primary crystallization, spray-drying and ageing to be explainedbelow.

What is important to the desired powderization of maltose is to take itscrystal form into account. The β-maltose monohydrated crystal isnonhygroscopic and the β-maltose anhydrous crystal is hygroscopic. Theα,β-complex crystalline maltose also has an advantage that it is not sodifferent from the β-maltose hydrate in hygroscopicity, easily solubleand easily crystallized from a viscous liquid. However, anomerizationproceeds as α,β-complex crystalline maltose takes up water and finallyturns to β-maltose monohydrate, from which the β-maltose monohydrate isconsidered to be the most stable form (Hodge, et al., Cereal ScienceToday, 1972). The β-form can easily be distinguished from the α-form bymeasuring the specific rotation.

In the method of the present invention, about 45% to about 55% ofmaltose contained in the saccharified solution (high purity maltosesolution) is precipitated as crystals or microcrystals at the primary orfirst crystallization step, and the resulting massecuite is spray-driedto evaporate most of the water, whereby the water content of thespray-dried product is made 5.5 to 7.5% which is larger than the 5%necessary for crystallization. At this point, about 20% to about 30% ofmaltose still remains in the form of α-anomer. For this reason, thesubsequent ageing step should include those conditions under whichabsorption of water necessary for crystallization, conversion toβ-anomer, formation of hydrated crystals and drying (removal of excesswater) can be effected. The present inventors have found that the ageingstep of the known methods focus only on drying so that a long period oftime is required. For example, according to Japanese Patent PublicationNo. 27325/1979 wherein a saccharified solution containing 7.5 to 11.5%of maltotriose is used for ageing, the ageing is conducted under theconditions that the solution is aged for 5 to 18 hours in 25° C.×60% RH,28° C.×64% RH and 30° C.×60% RH which correspond to 10 to 16 g water/kgdry air of absolute humidity, and then for 12 to 16 hours in alow-humidity air. In order to carry out such a prolonged ageing,equipment-related costs are very high.

The present inventors have extensively studied with an emphasis onconverting to β-maltose monohydrate crystals in as short a time aspossible, and have found that the foregoing water absorption,β-anomerization, formation of hydrated crystals and drying can becarried out in a short time under limited high temperature/high humidityconditions.

The dried powdery maltose was measured with respect to the followingfour properties: (1) hygroscopicity, (2) equilibrium water content, (3)free-flowability and (4) specific rotation.

The hygroscopicity was tested by allowing the test sample to stand for 1to 7 days at 30° C. and a relative humidity of 80%, during which thewater gain was measured with the lapse of time. In this test, the watercontent at the time of equilibrium was indicated as equilibrium watercontent. The free-flowability was judged in terms of the following fourgrades, A, B, C and D, according to the state of the test sample after24 hours of the above hygroscopicity test:

A: Keeps the same free-flowing powdery form as at the start of thehygroscopicity test.

B,C,D: Lumps are formed, and whether or not the lumps easily collapse isobserved.

The specific rotation was determined as follows: Five grams (on drybasis) of the sample was dissolved in 50 ml of dimethylformamide (DMF),and optical rotation was measured on the layer of 200 mm thick of thesolution and its five-fold value was indicated as specific rotation[α]_(D).

The powderization steps of the present invention will be successivelyexplained in more detail as follows. The sugar composition ofsaccharified solution, as described above, shall be as follows:Maltotriose content, not more than 2.5% and maltose content, not lessthan 90%. This solution is concentrated to precipitate primary maltosecrystals.

A thermostable α-Amylase (SPITASE HS Nagase & Co., Ltd.) was caused toact on a liquefied starch solution (20% starch content), as obtained bythe well-known mechanical liquefaction method, at 105° C. to make thedegree of hydrolysis 1.3. The solution, after being adjusted to a pH of4.5, was saccharified at 60° C. for 24 hours with the addition of acommercial β-amylase of soybean origin. The saccharified solution, afterbeing purified by the usual method, was separated into a maltosefraction and an oligosaccharide fraction by chromatography of asimulated moving bed system with a Na type cation-exchange resin. Bymixing both fractions in various proportions maltose solutions havingdifferent maltotriose content were prepared. The powderizationexperiment was carried out using these solutions according to the methodof the present invention. The results are shown in Table 1.

                                      TABLE 1                                     __________________________________________________________________________    Comparison of powderization of maltose solutions                              having different maltotriose contents                                         Sample     A        B         C                                               __________________________________________________________________________    Sugar compo-                                                                  sition (%)                                                                    Glucose    1.0      1.0       1.0                                             Maltose    90.9     89.6      90.4                                            Maltotriose                                                                              0.5      2.5       4.0                                             G.sub.4 or higher                                                                        7.6      6.9       4.6                                             Condition for rate                                                                       Bx 72.0, Bx 74.8   Bx 79.8                                         of crystallization to                                                                    30° C., 12 hours                                                                30° C., 12 hours                                                                 30° C., 12 hours                         reach 50 ± 5%                                                              Degree of supersatu-                                                                      1.52     1.58      1.70                                           ration of the maltose                                                         solution                                                                      Viscosity of the same                                                                    11200    83500     1160000                                         solution as above                                                             (c.p.)                                                                        Spraying condition                                                                       Direct spraying                                                                        Diluted to Bx 72                                                                        Diluted to Bx 68                                                    with a Bx 49/30° C.                                                              with a Bx 49/30° C.                                          maltose solu-                                                                           maltose solu-                                                       tion and sprayed                                                                        tion and sprayed                                                    30500 cp 30° C.                                                                  20800 cp 30° C.                          Ageing condition                                                                         60° C., 65% RH,                                                                 60° C., 65% RH,                                                                  60° C., 65% RH,                                     2 hours  2 hours   2 hours                                         Product                                                                       Equilibrium                                                                                7.51%    8.07%     9.12%                                         water content                                                                 Specific rota-                                                                           +115.0   +118.0    +119.8                                          tion [α].sub.D                                                          Free-flowability                                                                         A        B         C                                               __________________________________________________________________________

The degree of concentration necessary for the primary crystallization isin the range of 65 to 80% (as solid content), and its lower values willsuffice when the maltose purity is higher and the maltotriose content islower.

As shown in Table 1, Bx 72 will suffice for a case wherein the maltosecontent is about 91% and the maltotriose content is less than 1%, andeven Bx 65 will suffice for a maltose content of about 95%. But, a Bxrange of 75 to 80 is essential when the maltotriose content is more than2%. The amount of seed crystals added is not a very important factor andgenerally, a range of 0.1 to 1.0% (as solid maltose based on the totalsugar) will be sufficient.

The crystallization temperature is preferably within a range of 25±5° C.in view of economy and operability.

The rate of crystallization needs to be advanced to 50±5%. The viscosityof a massecuite at the point when the primary crystallization has beenfinished varies largely depending upon the content of maltotriose. Whenthe massecuite has a viscosity of less than 30,000 cp (at thecrystallization temperature), it may be subjected at once to spraydrying. When the massecuite containing the primary crystals has aviscosity higher than that, it is diluted to a viscosity of less than70,000 cp, preferably about 30,000 cp, by mixing the same with a properamount of a maltose solution of the same temperature as the massecuiteobtained by concentrating a saccharified solution of the same sugarcomposition until the saturation (but before the crystallization) ofmaltose contained therein, and then subjected to spray-drying.

As a spray drier, there may be used any of a rotating disc atomizer typeand a nozzle atomizer type, and the hot air flow in the drier may be anyof a horizontal parallel flow, a vertical downward parallel flow and avertical mixed upward flow. Preferably, however, combinations of arotating disc type atomizer and a vertical downward parallel flow orvertical mixed upward flow are used. The temperature and flow rate ofdry hot air and the flow rate of massecuite should properly becontrolled so that the water content of the resulting dry powder iswithin a range of 5.5 to 7.5%. Consequently, the flow rates of dry hotair and massecuite are determined on condition that the temperature ofhot air is within a range of 80° to 120° C.

The next important point concerns the ageing conditions after spraydrying. All the powders obtained by spray drying are not yet in fullygrown-up β-maltose monohydrated crystalline form, and about 20 to about30% of α-maltose is contained in the maltose powder.

A powdery maltose was prepared by concentrating a saccharified solution(sugar composition: maltose content 92.5% and maltotriose content 2.2%)to a concentration of 75% to carry out primary crystallization,spray-drying the resulting massecuite (water content 5.5 to 6.0%) andageing the resulting powder under a condition, 30° C.×55% RH, similar tothe well-known ones. The hygroscopicity test (after standing for threedays) and free-flowability test (after standing for one day) werecarried out on the powdery maltose to determine the required ageingtime. The results are collectively shown in Table 2, from which it hasbeen found that all the samples required a long ageing time of 10 hoursor longer.

The hygroscopicity test on a commercial powdery maltose (water content,6.33%) was also carried out at the same time, and it was found that thewater gain was 2.93% after one day, 3.20% after two days and 3.25% afterseven days, which shows that the maltose was stabilized after it tookabout 3% water. The equilibrium water content at that time was 9.3%.

                                      TABLE 2                                     __________________________________________________________________________    Ageing time at 30° C. × 55% RH                                                                             Time required                          Crystalline                            for formation                       Test                                                                             state before                                                                         Ageing time (hours)             of β-hydrated                  No.                                                                              ageing 2   4   6   8   10  12  16  18  crystals (hrs.)                     __________________________________________________________________________    1  Normal 1.55 D                                                                            1.37 C                                                                            1.32 C                                                                            1.37 B                                                                            1.23 A                                                                            1.20 A                                                                            1.23 A  10                                     crystal                                                                    2  Microcrystal                                                                         1.35 C                                                                            1.23 C                                                                            1.25 B                                                                            1.28 B                                                                            1.22 A                                                                            1.10 A                                                                            1.21 A  10                                  3    "    1.34 C                                                                            1.29 C                                                                            1.21 B                                                                            1.28 B                                                                            1.26 A                                                                            1.14 A                                                                            1.11 A  10                                  4  Normal 1.08 D                                                                            1.06 D                                                                            1.03 C                                                                            1.12 B                                                                            0.93 A                                                                            1.04 A                                                                            1.02 A  10                                     crystal                                                                    5  Normal 1.18 D                                                                            1.08 D                                                                            1.12 D                                                                            1.02 D                                                                            1.07 D                                                                            0.95 D                                                                            0.36 B                                                                            0.49 A                                                                            18                                     crystal                                                                    6  Microcrystal                                                                         1.04 D                                                                            1.10 D                                                                            0.97 D                                                                            0.93 D                                                                            1.06 D                                                                            1.12 D                                                                            1.16 A                                                                            1.17 A                                                                            16                                  __________________________________________________________________________     Remarks:                                                                      In the table, numerical values at the left hand show the hygroscopicity       rate (%) and symbols at the right hand show freeflowability              

In view of the above, the present inventors have studied a wide range ofthe temperature/humidity conditions and, unexpectedly, have found thatparticular high temperature/high humidity conditions outside theconventional recognition are much more preferable for ageing to attainthe object of the present invention. Thus, the present inventors havecarried out ageing under various conditions of 40° C. to 80° C.(temperature)×40 to 70% (RH), taking samples with the lapse of time andmeasuring specific rotation, water content, hygroscopicity andfree-flowability of the product. The results are shown in part in FIGS.1 and 2. FIG. 1 shows the specific rotation after 2 hours' ageing andFIG. 2 the water content after 2 hours' ageing. By overall judgementfrom these results, it has been found that, when thetemperature×humidity condition is 50° C.×preferably 60-70% RH, 60°C.×preferably 50-70% RH or 70° C.×preferably 50-70% RH, a completelyaged powdery maltose stabilized in both β-anomerization and watercontent is obtained by the ageing time of only 2 hours or shorter.

Contrary to this, at temperatures lower than 50° C., bothβ-anomerization and drying take a long period of time and fail to attainthe object of the present invention. Under higher temperature (exceeding75° C.)/high humidity conditions, not only both β-anomerization anddrying take a long period of time, but also a slight change intemperature (e.g. change in atmospheric temperature) during operationproduces condensed water, so that such temperatures are not practical.

When the humidity is as low as less than 50% RH, drying can be carriedout sufficiently, but β-anomerization takes a long period of time.Consequently, drying is finished before the completion ofβ-anomerization, so that the desired stable maltose powder is notobtained.

As described above, the particular powderization conditions in theageing after spray-drying of the present invention have not been knownbefore. The process is characterized in that, by carrying out ageing inthe high temperature/high humidity conditions of such limited range asspecified above, all of the water absorption necessary for spray-driedpowders for crystallization, β-anomerization, formation of hydratedcrystals and drying (removal of excess water) is attained in an ageingtime of only 2 hours or less, whereby stabilized free-flowablecrysatlline powdery maltose of low hygroscopicity can be obtained. Thisis therefore very useful in designing a continuous process.

As a result of free-flowability and hygroscopicity tests on the testsamples thus obtained, the following was further found: The ageing needsto be carried out in an atmosphere satisfying the condition that thetemperature be 50° to 75° C., relative humidity be 50 to 70%, andabsolute humidity be 45 to 185 g water/kg dry air. Under this condition,water absorption takes place for the first 30 minutes and then excesswater is removed by drying, whereby stabilized low-hygroscopicitypowdery maltose crystals having a water content of 5 to 7% and specificrotation of less than [α]_(D) +118° (DMF, dry basis) can be produced.

Of these ageing conditions, the most preferred one is 60° to 70° C. andRH 62 to 68% and 90 to 150 g water/kg dry air of absolute humidity.Under this condition, stabilized low-hygroscopicity crystalline maltosepowder having a water content of 5 to 6% and specific rotation [α]_(D)of 114 to 117 can be produced with a good reproducibility.

What is further preferable is that the powder should uniformly be agedat any portion in the high temperature high humidity. The ageing testwas carried out as follows. The spray-dried sample was placed in acylindrical vessel equipped with a wire net at the bottom in varyinglayer depths of 5, 10 and 20 cm, and aged while passing hot air throughthe wire net from the bottom so that the atmosphere in the vessel was60° C.×65% RH (absolute humidity, 91 g water/kg dry air). As a result,it has been found that complete anomerization from α-maltose toβ-maltose takes about 1.5 hours for a depth of 5 to 10 cm, and about 2hours for that of 20 cm. Further, also from the results ofhygroscopicity test, sensory test and water content test, it has beenfound that, with the column type ageing apparatus, the sample layer cannot be more than 20 cm in depth. The present inventors thus have foundthat it is preferred to use a moving belt conveyer or fluidized-bed typeageing apparatus so that the ageing step comprising water absorption,anomerization and crystallization can be carried out continuously anduniformly in the atmosphere described above.

Therefore in a preferred embodiment of the present invention, the drypowder coming out of the spray-dryer is immediately discharged onto acontinuous fluidized bed type ageing apparatus in a thin layer and iscontinuously passed through an atmosphere satisfying the above mentionedhigh temperature-high humidity conditions until the desired ageing iscompleted. When the aged product has a high moisture content (e.g. morethan 7%) it is preferable to dry the same to a moisture content of5-6.5%. This drying can also be conducted continuously with hot-air by abelt-conveyor or fluidized bed type drier.

The invention will be illustrated further specifically with reference tothe following examples.

EXAMPLE 1

A liquefied starch solution of a low degree of hydrolysis [dextroseequivalent (DE), 6.0] was prepared by causing α-amylase (SPITASE HS,produced by Nagase & Co., Ltd.) to act on a 30% aqueous solution ofcommercial corn starch (produced by Sanwa Denpun K.K.) according to thewell-known method. To the solution was added a commercial β-amylase ofsoybean origin (produced by Nagase & Co., Ltd.) in an amount of 0.2%based on the starch (as dry basis), and the saccharification reactionwas carried out at pH 5.0 and at 60° C. for 24 hours to obtain asaccharified solution of a sugar composition of 60% maltose and 9.8%maltotriose. The resulting solution, after being subjected tofiltration, decoloration, purification with ion-exchange resin andconcentration by the usual method, was freed from oligosaccharides bysimulated moving bed system chromatography on Na-type cation-exchangeresin (Mitsubishi Chemical Industries, Ltd.) to obtain a high-puritymaltose solution (fraction) corresponding to 58% of the total sugar. Thesugar composition of this high-purity maltose solution determined byhigh-performance liquid chromatography (HPLC) is as follows:

    ______________________________________                                               Glucose 1.0%                                                                  Maltose 90.9%                                                                 Maltotriose                                                                           0.5%                                                                  DP ≧ 4                                                                         7.6%                                                           ______________________________________                                    

This solution was concentrated to Bx by 72 by vacuum concentration, and5 kg of the resulting concentrate was charged to a closed vessel typecrystallizer (6 liters in volume) equipped with atemperature-controlling jacket and a stirrer. At the point when thetemperature of the solution reached 30° C. (degree of supersaturation ofmaltose, 1.52), seeds (β-maltose monohydrate-containing massecuite ofthe same composition as that of the above concentrate) were added at arate of 0.5% (as converted to the dry maltose basis) based on the solidcontent of the solution, and primary-crystallization was carried out at30° C. for 12 hours at 80 rpm. The massecuite obtained by thecrystallization was found to contain β-maltose hydrate fine crystals(triangular plate like crystals of about 20μ in size by microscopicobservation) and the crystallization degree was 48%, as converted to thedry maltose basis, based on the solid content of the massecuite. Theviscosity of the massecuite was 11,200 cp (B-type viscometer). Thismassecuite was directly dried in a spray-drier comprising a rotatingdisc type atomizer and a vertical downward parallel flow type blowerwhile maintaining the hot air inlet at 80° C., to obtain a flowingpowder having a water content of 6.2%.

This powder was immediately spread in a thickness of about 0.5 to about1.0 cm in a constant-temperature/constant-humidity oven kept at 60° C.and 65% RH (absolute humidity, 91 g water/kg dry air), and aged for 2hours. The powder after ageing had a water content of 6.4% and aspecific rotation [α]_(DMF) of +115.0°, and showed little hygroscopicityeven in an atmosphere of 30° C.×80% RH and kept a powdery form excellentin flowability. The equilibrium water content in the same condition was7.5%.

EXAMPLE 2

In the same manner as in Example 1, a high-purity maltose solution of asugar composition of 89.6% maltose and 2.5% maltotriose was obtained.

This solution was concentrated to Bx 74.8 and primary-crystallized for12 hours in the crystallizer described above under the conditions thatthe temperature of the solution is 30° C. (degree of supersaturation ofmaltose, 1.58); amount of seed is 0.5% and a number of rotations is 80rpm.

The massecuite on completion of the primary-crystallization was found tocontain a large number of β-maltose hydrate fine crystals and the degreeof crystallization was 47%. The viscosity was 83,500 cp. This massecuitewas diluted to Bx 72 by mixing with 11% (based on the massecuite) of aBx 49 solution of the same composition and temperature, so as to have acrystal content of 47% and a viscosity of 30,500 cp. The resultingmassecuite was spray-dried in the same manner as in Example 1 to obtaina powder having a water content of 5.8%. Immediately thereafter, thepowder was aged for 2 hours on a fluidized-bed type ageing apparatus inan atmosphere of 60° C.×65% RH, and then dried for 2 hours in a hot-airdrier kept at 40° C. to obtain a powdery maltose.

This powder had a water content of 6.2% and a specific rotation[α]_(DMF) of +118.0°, showed little hygroscopicity under a condition of30° C.×80% RH and kept a powdery form excellent in flowability.

EXAMPLE 3

A liquefied starch solution of a low degree of hydrolysis (DE 1.0), asprepared in a manner similar to Example 1 using a 20% aqueous slurry ofcommercial potato starch, was saccharified for 72 hours to obtain asaccharified solution of a sugar composition of 70% maltose and 6%maltotriose. The resulting solution, after being subjected tofiltration, decoloration, purification with ion-exchange resin andconcentration by the usual method, was freed from oligosaccharides bysimulated moving bed system chromatography on Na-type cation-exchangeresin to obtain a high-purity maltose solution (fraction) with a sugarcomposition of 96.2% maltose and 1.1% maltotriose. The yield of maltosein the maltose fraction was 62% based on the total sugar. The maltosesolution thus obtained was concentrated to Bx 65 andprimary-crystallized for 12 hours under the conditions that thetemperature of the solution is 20° C. (degree of supersaturation ofmaltose, 1.59) the amount of seed is 0.5% and the number of rotations is80 rpm. The massecuite thus obtained had a degree of crystallization of52% and a viscosity of 25,000 cp. This massecuite was directlyspray-dried while keeping the hot air inlet at 80° C., to obtain apowder having a water content of 5.5%. This powder was then aged for 2hours in a closed type constant-temperature/constant humidity oven keptat 60° C. and 65% RH to obtain a powdery maltose.

This powder had a water content of 6.0% and a specific rotation [α]_(D)+114° (DMF, dry basis), showed little hygroscopicity under the conditionof 30° C.×80% RH and kept a powdery form excellent in flowability. Theequilibrium water content in the same condition was 6.5%.

EXAMPLE 4

This example illustrates the production of powdery maltose on anindustrial plant capable of producing powdered crystalline maltose ofabout 80 tons/day.

A corn starch slurry having a concentration of 25%, after adjusting itspH to 6.0, was liquefied in the same manner as in Example 1 on acontinuous J-cooker with addition of a proper amount of bacterialα-amylase. The resulting liquiefied solution of DE 6.0 was saccharifiedat 55° C. for 48 hours with addition of β-amylase and pseudomonasisoamylase. The resulting saccharified solution had the following sugarcomposition: Maltose, 75%; glucose, 0.5%; maltotriose, 15%; and therest, maltooligosaccharides which are a higher-order polymer thanmaltotetrasaccharide. This solution was purified as usual with activatedcarbon and ion-exchange resin, and concentrated to a concentration of60% on an evaporator.

In the same manner as in Example 1, the concentrate was separated into amaltose fraction and an oligosaccharide fraction by simulated moving bedsystem column chromatography on Na-type cation-exchange resin.

The maltose fraction corresponded to 65% of the total sugar, and itssugar composition was 95% of maltose, 2% of maltotriose and 1% ofglucose. This fraction was concentrated to Bx 68% on an evaporator andtransferred to the 1st crystallizer, and after adding 0.5% of seedcrystals, kept at a constant temperature of 30° C. for 12 hours withstirring. The degree of crystallization after 12 hours was 47%, and theviscosity of the resulting massecuite was 62,000 cp.

The massecuite was dried on a spray-drier to obtain a powder having awater content of 5.1%. The spray-drier used here was a large-sized oneof the same type as used in Example 1 comprising a rotating disc typeatomizer and a vertical parallel downward flow type blower. In thiscase, the massecuite was supplied to the atomizer from the upper part ofthe drying chamber by means of a usual pump. The downward flow of hotair was passed in parallel with the flow of the massecuite. The inlettemperature of hot air was kept at 95° C. and the outlet temperature was74° to 75° C. on a normal run. The spray-dried product was continuouslywithdrawn from the bottom of the drying chamber and immediatelytransferred to the subsequent ageing step. As the ageing apparatus therewas used a continuous fluidized-bed type ageing apparatus. Theatmosphere in the apparatus was adjusted to 65° C.×70% RH. The timerequired for the spray-dried product to pass through the ageingapparatus was fixed to 4 hours. During this period, water absorption,conversion to β-anomer and formation of hydrated crystals were carriedout. The water content of the aged product at the outlet was 7.2%. Thisproduct was then led to a belt conveyor type drier wherein it was driedinto a final product by hot air. The physical properties of the finalproduct were as follows: Water content, 6.1%; free-flowability, A(free-flowing powdery form); and specific rotation [α]_(D) +115° (DMF,dry basis).

Incidentally the fluidized bed type ageing apparatus is similar to awell known fluidized bed dryer except that a temperature and humiditycontrolling device is associated therewith in place of a hot-air blower.The said apparatus may be batchwise, but continuous type is preferablefor large scale industrial production.

What is claimed is:
 1. A method of producing powdery crystalline maltosecharacterized by a high concentration of the beta-anomer of maltosemonohydrate comprising the steps of(1) obtaining a high purity maltosesolution with a sugar composition of not less than 90% of maltose andnot more than 2.5% of maltotriose by enzymatic saccharification of aliquefied starch solution characterized by a low degree of hydrolysis,(2) concentrating said high purity maltose solution to a solid contentof 65 to 80%, (3) adding seed crystals containing beta-maltosemonohydrate to the concentrated solution, (4) conducting a primarycrystallization whereby maltose monohydrate crystals are precipitated ata temperature of 25±5° C. until the degree of crystallization reaches50±5%, (5) spray drying the resulting massecuite to obtain a powderyproduct having a water content of 5.5-7.5%, and (6) aging the powderproduct by exposing it immediately after the spray-drying to anatmosphere wherein the temperature is 50°-75° C., the relative humidityis 50-70%, and the absolute humidity is 45-185 g water/kg dry air toconvert alpha-maltose to beta-maltose and complete the crystallizationof maltose monohydrate.
 2. A method as claimed in claim 1 wherein, whenthe viscosity of the massecuite after the primary crystallization is toohigh, a proper amount of a maltose solution is added thereto to lowerthe viscosity of the massecuite at the crystallization temperature toless than 70,000 cps, before subjecting the resulting massecuite to thespray-drying.
 3. A method as claimed in claim 1 wherein, after theenzymatic saccharification, the saccharified solution is separated intoa high purity maltose-containing fraction and anoligosaccharide-containing fraction by simulated moving bed systemchromatography with a cation-exchange resin, to obtain the high puritymaltose solution.
 4. A method as claimed in claim 1 wherein thespray-drying is conducted by the use of a parallel flow type spray-drierwith a rotating disc type atomizer, the inlet hot air temperature being80°-120° C.
 5. A method as claimed in claim 1 wherein the aging isconducted continuously on a continuous belt conveyor type or continuousfluidized bed type ageing apparatus.